Process and device for enriching water with magnesium ions

ABSTRACT

The invention relates to a process and a device for enriching water, in particular drinking water, with magnesium ions. In order to enable enrichment of water with magnesium ions in exchange for calcium ions and/or heavy metal ions during treatment of water, and in particular of drinking water, it is proposed according to the invention to pass the water through an ion exchanger which contains a weakly acidic ion exchange material, wherein at least a part of its ion exchange capacity is loaded with magnesium ions.

RELATED APPLICATIONS

This application is a continuation application of InternationalApplication PCT/EP2007/062854. filed Nov. 27, 2007. which claimspriority to DE 10 2006 058 223.3, filed Dec. 1, 2006, which are herebyincorporated by reference in their entirety.

BACKGROUND

The invention relates to a process and a device for enriching water, inparticular drinking water, with magnesium ions.

In order to protect installations such as pipelines, hot watergenerators and fittings from incrustation and corrosion caused by waterwhich flows through them, the water is customarily treated. Since theincrustations are caused mostly by deposits of salts of hardnessproducing substances such as calcium and magnesium, softening equipmentis usually employed to protect such installations. This equipmentremoves calcium and magnesium ions from the water. The function of thesoftening equipment is usually based on the ion exchange principle,whereby calcium and magnesium ions are either fully or partiallyreplaced by sodium or potassium ions from an ion exchanger. In order toprotect the installations from corrosion, corrosion protection agentscan be added to the water in the form of polyphosphates and/ororthophosphates, silicates, carbonates and/or hydroxides, typicallyusing a dosing system.

In addition to treatment of water performed in pipelines or other watersupplying installations, other methods are used in which the water istreated directly at the tap location. This type of water processingoperation carried out directly at the tap location, and sometimes alsoin separate containers, is referred to as processing at the point of use(“POU”). The systems used in POU processing are either arranged directlyin front of or at the tap. Alternatively, open systems can be employedin which the water is processed in separate containers, typically cans.

Equipment for water processing operations is installed at the taplocation directly at the outlet cock or just in front of it. Fortreatment of water in separate containers, it is known to use systems inwhich an insert or an attachment for a container is filled from abovewith the water to be processed, so that the water then flows through afine filter in order to remove particles, and through activated carbonso as to remove chlorine, flavor imparting substances and odoroussubstances. The water then flows through an ion exchanger in a lowerpart of the container to remove hardness producing substances such ascalcium and magnesium ions, heavy metals and hydrogen carbonate. Thesecontainers are known commercially as so-called “pitchers” or “jugs” andthey are offered, for example, by the firms Anna and Brita.

The ion exchangers used in these containers contain mostly weakly acidiccation exchange resins in which the hardness producing substances andheavy metals present in drinking water are for the most part replacedwith hydrogen ions from the ion exchanger. A consequence of thisreplacement is that the processed drinking water has a pH value in theapproximate range of 4.5 to 5, while unprocessed drinking water or tapwater mostly has a pH value of more than 7.

This lowering of the pH value by these commercial containers hasconsequences when the water processed in the container is used, as isoften the case, not for drinking or cooking, but also for preparation ofdrinks using hot water, in particular, to make tea. Since only the pHvalue of the water, and not the ingredients of the tea, is responsiblefor the color of the tea, such tea becomes brighter and clearer as thepH value of the water is lowered. This is because tea leaves containcatechins, chlorophyll and flavonoids, which are natural pH indicators.

If the pH value is less than 4, the poured tea will be colorless. Whenthe water has a pH of more than 7, the tea is darker, and oxidation ofpolyphenols which are contained in the tea leaves occurs at the sametime. The polyphenols become crosslinked to polymers, which areinsoluble in water and which form a thin film on the surface.

For this reason, weakly acidic cation exchange resins are employed in abuffered form in order to prevent lowering the pH value during ionexchange. In this buffered form they are conditioned or loaded to acertain extent with sodium ions or also with potassium ions, while therest remains in the form of hydrogen ions. However, the total cationload of the raw water is not replaced during the exchange by hydrogenions, since some of it will be replaced by sodium ions or potassiumions. The pH value of the processed water can be adjusted with this typeof buffering to a value of more than 6.

However, it can be generally said that as a result of this treatment ofwater, physiologically important magnesium ions are removed, to agreater or lesser extent, from drinking water, which causes the qualityof the drinking water to deteriorate. Moreover, the increase of thesodium content in drinking water is considered detrimental, inparticular when the processed drinking water is used for preparations ofmeals for infants.

It is known in the art that calcium ions contained in drinking water canbe exchanged for magnesium ions by means of ion exchangers with astrongly acidic exchange resin. In this context, a method is described,for example, in DE 100 20 437, wherein an ion exchanger is regeneratedwith a strongly acidic cation exchange resin, for example, by means of asolution of magnesium chloride. After the regeneration, the stronglyacidic exchange resin of the ion exchanger is in the form of magnesiumand can then release its magnesium ions in exchange for calcium ionsduring the preparation of drinking water. After the cationic ionexchange resin has been exhausted, the ion exchanger can again beregenerated with a magnesium chloride solution.

However, in contrast to a strongly acidic cationic ion exchange resin, aweakly acidic cationic exchange resin cannot be regenerated by means ofa salt solution, such as, for example, with magnesium chloride. Weaklyacidic cationic exchange resins which exist after an application forsoftening of water in the calcium form, namely, so that they areessentially loaded at 100% of their ion exchange capacity with calciumions, are exhausted, and they can be regenerated only with acids. Thisis due mainly to the fact that weakly acidic cationic exchange resinscontain as a rule carboxyl groups in the form of strong ions orexchange-active groups, onto which the calcium ions bond in the calciumform. The calcium ions are therefore only slightly dissociated in theion exchanger and they are exchanged for the hydrogen ion of the acid.After the regeneration with an acid, the exchanger is again in the formof hydrogen ions, i.e., it is essentially loaded up to 100% of its ionexchange capacity with hydrogen ions.

Weakly acidic ion exchange resins can be conditioned after regenerationwith an acid in a further preparatory stage, wherein they are converted,for example, with a sodium hydroxide solution or caustic potash solutioninto the sodium form or the potassium form, in which they are loadedwith sodium ions or potassium ions instead of hydrogen ions.

It is also known from prior art that conditioned weakly acidic cationicexchange resins can be used in order to remove other cations, forexample, ions of heavy metals or ions of hardness producing substances,from water. In this case, the heavy metal ions or ions of hardnessproducing substances are exchanged for sodium ions or potassium ions.However, if a weakly acidic cationic exchange resin is in the calciumform, an exchange of cations is no longer possible, with the exceptionof hydrogen ions.

SUMMARY

The present invention provides a process and device for treatment ofwater, in particular, for treatment of drinking water, in which thedisadvantages described above do not occur and which enriches water withmagnesium ions.

This task is achieved by conducting the water through an ion exchangerwhich contains a weakly acidic ion exchange material, and preferably aweakly acidic cationic exchange resin, which has its ion exchangecapacity at least partially loaded or enriched with magnesium ions.

The term a “weakly acidic ion exchanger material” or “cation exchangeresin” should be understood within the scope of the present inventionmaterial such as the material which is described among others byHartinger, Ludwig, in “Handbook of Water and Recycling Technology forMetal Processing Industry,” Carl Hanser Publishing House, Munich, Vienna1991. According to Chapter 5.2.3.3 of this handbook, the firstdistinction to be made with respect to ion exchange resins is whetherthese ion exchange resins are cation exchangers or anion exchangers,which depends on which exchange-active group is contained in the resin.This group can be then further differentiated depending on whether thecation exchangers are strongly acidic and weakly acidic. Strongly basicand weakly basic exchange resins are differentiated in the case of anionexchangers. The ion exchangers then exhibit the corresponding conductduring the exchange reaction, namely, as strong or weak acids or asstrong or weak bases. Accordingly, weakly acidic cation exchangersexhibit the conduct of weak acids, and as such, form a mostlyundissociated form, in which they are hardly able to adsorb any othercations.

Surprisingly enough, it has been found that it is possible to quiteeasily exchange magnesium ions by means of a weakly acidic cation ionexchanger for calcium ions and even for heavy metal ions.

This fact is surprising to the extent that since calcium and magnesiumare alkaline earth metals with very similar characteristics, one wouldexpect that magnesium ions would form complexes in the same manner as docalcium ions with the exchange-active carboxyl group of weakly acidiccation exchange resins, which is why dissociation is not present in thematrix of strong ions of the weakly acidic cation exchanger. Thisconclusion is obvious also to the extent that it is known in the fieldof detergents that in order to prevent depositing by means ofcarboxylates, a complexation can be produced which contains both calciumions and magnesium ions because both types of ions display a similarconduct in the complexation. This would, however, mean that an exchangeof magnesium ions of the cation exchanger for other cations would not bepossible, with the exception of hydrogen ions.

However, it was possible to prove that a similar exchange is indeedpossible with the process and device according to the invention, whichcan be utilized according to a preferred embodiment of the invention fortreatment of drinking water in order to achieve depletion of calciumand/or heavy metal ions present in water with the simultaneousenrichment of water with magnesium ions.

It was determined during tests that magnesium ions are present in aweakly acidic cation exchanger in a much more strongly dissociated formthan calcium ions, i.e., they do not enter into a strong bond, incontrast to the calcium ions having carboxyl groups of the weakly acidiccation exchanger. Therefore, since no acid is required for thedissociation of magnesium ions during the exchange reaction orregeneration of the cation exchanger, a weakly acidic cation exchangerwhich is loaded with magnesium ions is capable of exchanging itsmagnesium ions for ions that are found in water, such as, for example,calcium, copper or lead ions. When such a weakly acidic cation exchangeris used in the magnesium form for treatment of drinking water,enrichment of the drinking water with magnesium ions will occur, whichwill replace, either entirely or partially, the other cations that arecontained in raw water, such as for example calcium, copper or leadions.

It is in principle in this case possible to convert weakly acidiccationic exchange material fully into the magnesium form, in which theion exchanger material is essentially loaded up to 100% of its ionexchanger capacity with magnesium ions. In this case, almost all thecations contained in drinking water will be exchanged during theexchanger reaction for the magnesium ions of the exchanger, whereby amaximum concentration of magnesium ions can be attained in drinkingwater. During the state when the substance is fully loaded withmagnesium, the exchange occurs without an appreciable change of the pHvalue.

An ion exchanger having a similar material which is loaded withmagnesium ions can be advantageously employed for processing of socalled gypsum waters, i.e., waters which have a high content of calciumand sulfate. These waters can lead to strong precipitations andsediments of poorly soluble calcium sulfate in pipelines, heat watergenerators and other water conducting equipment. However, when thecalcium ions contained in the water are exchanged in accordance with theprocess of this invention for magnesium ions, the processed watercontains easily soluble magnesium sulfate instead of the poorly solublecalcium sulfate, which clearly reduces the risk of precipitants andsediments.

For the employment of the process in accordance with the invention atthe point of use (POU), however, an exemplary embodiment is providedwherein the weakly acidic cation exchanger is only partially loaded withmagnesium ions with respect to its ion exchange capacity. This isbecause a weakly acidic cation exchanger which is only partially loadedwith magnesium ions will replace only one part of the calcium ionscontained in water by magnesium ions, but it will still remove almostall heavy metals, while at the same time, the pH value of the treatedwater can be adjusted to a desired value somewhat below 7. In addition,the time required for the loading of the exchanger material can bereduced in this manner.

Since the pH value of the treated water depends on the extent to whichthe ion exchanger material is loaded with magnesium ions, or on theextent of the loading with the hydrogen ions, one can, for example,advantageously adjust the pH value for preparation of tea to a value ofless than 7.0, and preferably to about 6.5, so that the weakly acidicion exchange material is conveniently loaded with magnesium ions in therange of about 30% to 70%, preferably in the range of about 50% to 60%of its ion exchange capacity, while the rest of the ion exchangermaterial is in the form of hydrogen ions, so that it is loaded withhydrogen ions in the range of 70% to 30%, and preferably in the range ofabout 60% to 50% of its ion exchange capacity. Under these conditions,the drinking water to be processed is enriched with magnesium ions,while the pH value can be at the same time lowered relative to asituation in which the ion exchange material is fully loaded withmagnesium ions.

For drinking water it is advantageous when the pH value of the treatedwater is raised above the value of 6.5 because the concentration ofmagnesium in the treated water is higher at higher pH values.

The initial loading of the weakly acidic cation exchanger with magnesiumor its regeneration preferably occurs by means of a suspension ofmagnesium oxide to which the cation exchanger is added so that thesuspension is stirred for a certain period of time.

BRIEF DESCRIPTION OF DRAWINGS

The FIGURE is a schematic side sectional view of a device for enrichingwater in accordance with the present invention.

DETAILED DESCRIPTION

The embodiments of the present invention described below are notintended to be exhaustive or to limit the invention to the precise formsdisclosed in the following detailed description. Rather, the embodimentsare chosen and described so that others skilled in the art mayappreciate and understand the principles and practices of the presentinvention.

The following is a detailed explanation of an embodiment of theinvention indicated in the drawing, wherein the single figure shows adevice for enriching water with magnesium ions.

The device or system shown in the drawing includes a container 1 whichis open at its upward end, as well as an insert 2 which serves forfiltration and treatment of drinking water, and which is suspended inthe expanded upper front end of the container 1.

The insert 2 includes an upper part 3 that extends upwards, and anupright, substantially cylindrical lower part having an exchangeable orreplaceable cartridge 4 having a cartridge housing which is insertedinto the upper part 3 of system or device 1. The cartridge is providedon its upper front end with one inlet opening 5 and on its lower frontend with a plurality of outlet openings 6. The cartridge 4 is penetratedin the upper part with a round receiving opening created in the bottom 7of the upper part 3, and it is sealed by means of an annular seal 8 inrelation to the upper part 3, so that no water can be introduced fromthe upper part 3 onto the cartridge 4 in the inner part of the container1. The upper part 3 forms a reservoir for the water to be treated, whichflows after the upper part 3 has been filled due to gravity through thecartridge 4 into the container 1. The cartridge 4 contains an ionexchanger 9, which has the form of a packing made of a weakly acidiccationic exchange resin loaded with magnesium ions, so that when thewater flows through the cartridge 4, calcium ions and heavy metal ionsobtained from the water are exchanged for magnesium ions from thecationic exchange resin and the treated water is thus enriched in thismanner with magnesium ions. At the upper end and at the lower end of thecartridge 4, respectively, is deployed a fine filter 10 or 11, whichprevents entry of contaminants such as particles contained in raw waterinto the ion exchanger 9, or the discharge of solid substances from thecartridge 4 through the outlet openings 6 provided in the container 1.

A cation exchanger of the Lanxess Company, type S 8227, was employed inthe lower part 3 of the insert 2 as the ion exchanger 9 during watertreatment tests performed with a similar container, which was loadedahead of time with magnesium ions so that it was loaded to about 60% ofits ion exchanger capacity with ions in the form of magnesium ions,while hydrogen ions were used for the remaining capacity.

In order to load the weakly acidic cation exchange resin of the cationexchanger with magnesium ions, the exchanger resin of the ion exchanger,which was first in the form of hydrogen ions, was processed in batch inan aqueous suspension of magnesium oxide (MgO) so that the suspensionwas stirred during a period of several hours.

During the subsequent tests, the cation exchanger was impacted by tapwater which contained calcium and magnesium ions, as well as copper ionsin different concentrations. The content of calcium ions and magnesiumions, or copper ions, was measured before and after the tap water passedthrough the cation exchanger in order to determine the success of theenriching of drinking water with magnesium ions, or the success of theremoval of heavy metal ions.

Tables 1 and 2 show the results of the tests with respect to theenriching of the water with magnesium ions, and the changes of the pHvalue and of the content of calcium ions for two different tap watertypes, wherein the pH value and the concentration of Ca⁺⁺ ions and Mg⁺⁺ions are indicated both for the inflow to and outflow from the ionexchanger depending on the volume of the processed water.

TABLE 1 Inflow to the Outflow from Ion Exchanger the Ion Exchanger WaterVolume Ca⁺⁺ in Mg⁺⁺ in Ca⁺⁺ in Mg⁺⁺ in in Liters pH ppm ppm pH ppm ppm 27.6 115 16.0 6.7 14.1 13.8 8 7.6 113 17.4 6.3 15.7 24.2 14 7.6 112 15.66.3 18.0 25.6 26 7.6 111 15.1 6.5 29.1 29.8 38 7.6 112 14.7 6.6 40.229.3 71 7.6 114 14.9 7.0 84.1 20.9 106 7.6 114 14.2 7.1 91.3 18.0 1267.6 114 14.2 7.2 97.8 16.1

TABLE 2 Inflow to the Outflow from Ion Exchanger the Ion Exchanger WaterVolume Ca⁺⁺ in Mg⁺⁺ in Ca⁺⁺ in Mg⁺⁺ in in Liters pH ppm ppm pH ppm ppm 27.4 80.4 8.78 6.7 7.8 0.3 5 7.4 68.2 5.20 6.4 9.2 10.5 10 7.4 63.7 3.776.4 11.8 14.0 21 7.4 63.5 3.83 6.5 15.5 15.7 61 7.5 62.9 3.92 6.8 32.612.8 106 7.5 69.4 5.31 6.9 39.6 14.8 123 7.4 69.6 5.94 6.9 50.3 9.9

As one can see from Table 1 and 2, one part of the calcium ionscontained in the water is exchanged during the passage of the waterthrough the ion exchanger for magnesium ions from the weakly acidiccation exchanger resin. Therefore, the concentration of the magnesiumions in the treated water is clearly above the concentration of themagnesium ions in the raw water. Further, it is also evident that the pHvalue of the water after the water has passed through the ion exchangeris at least 6.3, which means that the water flowing out of the ionexchanger is particularly suitable for preparation of tea.

Table 3 shows the results of tests carried out with different tap waterwith respect to enriching with copper ions in water, enriching withmagnesium ions in water, and changes in the content of calcium ions,wherein depending on the volume of the treated water, the concentrationof the Ca⁺⁺, Mg⁺⁺ and Cu ions are indicated during the inflow to andoutflow from the ion exchanger.

TABLE 3 Inflow to the Outflow from Ion Exchanger the Ion Exchanger WaterVolume Ca⁺⁺ in Mg⁺⁺ in Cu⁺⁺ in Ca⁺⁺ in Mg⁺⁺ in Cu⁺⁺ in in Liters ppm ppmppm ppm ppm ppm 3 116 23.4 2.09 22.9 26.0 0.11 16 118 24.8 2.19 59.035.0 0.13 40 119 24.7 2.13 83.2 27.9 0.24

As one can see from Table 3, the weakly acidic cation exchanger of theexchange resin was capable of exchanging more than 90% of the copperions contained in water for hydrogen or magnesium ions.

It was then determined during further tests that the same was true alsoabout other heavy metal ions, such as for example lead ions, which werealso exchanged for magnesium ions.

In summary, one can say that an ion exchanger having a weakly acidiccation exchange resin makes it possible to remove both calcium and heavymetal ions from raw water and replace them with magnesium ions.

Unlike with an ion exchanger which has a weakly acidic cationic exchangeresin in the form of hydrogen ions and which exchanges only cations thatstoichiometrically correspond to the hydrogen carbon ions, cations ofcorresponding sulfates, nitrates and chlorides are additionally alsoexchanged.

While exemplary embodiments incorporating the principles of the presentinvention have been disclosed hereinabove, the present invention is notlimited to the disclosed embodiments. Instead, this application isintended to cover any variations, uses, or adaptations of the inventionusing its general principles. Further, this application is intended tocover such departures from the present disclosure as come within knownor customary practice in the art to which this invention pertains andwhich fall within the limits of the appended claims.

What is claimed is:
 1. A process for treating drinking water,comprising: providing an ion exchanger which contains a weakly acidicion exchange material, the ion exchange material being loaded at leastto a part of its capacity with magnesium ions and loaded in the range of70 to 30% of its capacity with hydrogen ions; conveying water throughthe ion exchanger, wherein calcium ions are extracted from the water inexchange against magnesium ions, and thereby producing drinking waterenriched with magnesium ions.
 2. The process of claim 1, wherein the ionexchange material comprises a weakly acidic cation exchange resin. 3.The process of claim 1, wherein the ion exchange material is loaded withmagnesium ions in the range of 30 to 70% of its ion exchange capacity.4. The process of claim 1, further comprising filtering the water beforeor after the water is conveyed through the ion exchanger.
 5. The processof claim 1, further comprising selecting the level of loading ofmagnesium ions such that the pH value of the conveyed water has a valueof 6.5 or higher.
 6. The process of claim 1, further comprisingselecting the level of loading of magnesium ions such that the pH valueof the conveyed water has a value of 7.0 or less.
 7. The process ofclaim 1, further comprising combining tea leaves with the treated waterfor preparation of hot tea, the tea having a color that is darker thanthe color of the untreated water.
 8. The process of claim 1, furthercomprising: providing a container having an opening at a top endthereof; positioning the ion exchanger within the container; filling thecontainer with the water through the top end; and allowing the water toflow through the ion exchanger via gravity.
 9. The process of claim 1,further comprising regenerating the ion exchange material with asuspension of magnesium oxide and water.